1. Field of the Invention
The present invention concerns an enameling lacquer and a process for the manufacture of the lacquer.
The invention is particularly but not exclusively applicable to enameling wire for use in the windings of electric motors or any other electrical components, the wire being applied by an automatic machine, for example.
2. Description of the Prior Art
In the case given of electric motor windings, it is imperative that the windings are as compact as possible and can easily be introduced into an appropriate housing without affecting the insulating properties of the lacquer.
Windings are produced at high speeds; the enameled conductor is subjected to friction and to severe mechanical stress which may damage the insulation and result in irregular winding of the conductor, for example during placement in stator winding slots. There could be serious effects on the insulation properties, service life and efficiency of the component.
A number of solutions have been proposed which are intended to reduce the coefficient of friction of enameled electrical conductors, to provide a smooth surface and to enable them to be wound easily.
A first solution consists in lubricating the exterior of the enameled conductor by coating the surface with a lubricating substance such as paraffin wax, oil, a natural or synthetic wax or polysiloxane. The results are inadequate and irregular.
A second solution consists in providing the conductor with an external layer of polyamide 6--6, trade name NYLON, well known for its slippery qualities. Results show that this process improves smoothness, but the nylon reduces the thermal characteristics of wires with a thermal index of greater than 200.degree. C.
A third solution consists in introducing an internal lubricating agent into the outer layer of a conductor. The polymers most frequently used for this application are aliphatic or aromatic polyamides, aromatic polyamide imides, polyester imides, polyimides, polyvinyl alcohol acetals, mixed aromatic/aliphatic polyamides, polyepoxy compounds and polyphenoxy compounds.
French patent FR-A-2 533 357 indicates how a lacquer can be made which incorporates in the polymer less than 0.3% of a particular form of internal solid lubricant. This technique uses a lubricant which is incompatible with the base polymer. This incompatibility effectively expels the lubricant particles onto the outer surface of the outer layer, improving its slippery qualities. Such a process is very difficult to carry out industrially, however. Mutual incompatibility of the two materials prevents incorporation of a sufficient quantity of lubricant, resulting in frequent irregularities in the conductor which are unacceptable to the user.
The aim of the present invention is to overcome these problems.